I guess if the pH of the drinking water is too much away from the 7 than there is something for sure in the water.
If the water is from a spring or a well, a pH higher than 7 will indicate that the water has some minerals in it. I have never done so but you could possibly pH test a mineral water and see if its pH is above 7.
I know many sites who sell pH drops of special water processing machines will claim that to alkalize one should drink alkaline water. I don't know if these are really helpful. I doubt that they can come close to the way the ML alkalizing drink will alkalize.